1. Field of the Invention
The present invention relates to an air-flow control device for an engine.
2. Description of the Related Art
Japanese Unexamined Patent Publication No, 63-143349 discloses an air-flow control device for an internal combustion engine having an intake passage and a fuel injector arranged in the intake passage for injecting fuel into the intake passage. The device includes an air-flow control valve arranged in the intake passage upstream of the fuel injector, and a driving apparatus for driving the air-flow control valve so as to close the air-flow control valve during an engine starting operation, and to open after the engine starting operation is finished.
In a typical engine having a throttle valve in the intake passage, when an engine starting operation is to be started, there exists a large amount of air in the intake passage downstream of the throttle valve, even if the throttle valve is substantially closed. In this condition, if the starting operation of the engine is started, this large amount of air is drawn into a combustion chamber of the engine, and thereby makes the air-fuel ratio in the combustion chamber extremely lean and causes improper combustion in the combustion chamber. As a result, a large amount of unburned HC could be exhausted into an exhaust passage of the engine. In particular, in an engine having a surge tank in the intake passage, a larger amount of air could be drawn into the combustion chamber at the starting operation of the engine, and thus, a larger amount of unburned HC could be exhausted into the exhaust passage. To solve this problem, in the air-flow control device mentioned above, the air-flow control valve is provided between the throttle valve and the fuel injector, and is made substantially closed to thereby prevent the combustion chamber from drawing a large amount of air during the engine starting operation. After the engine starting operation is finished, the air-flow control valve is made open so that a proper amount of air can be drawn into the combustion chamber.
In this connection, in the air-flow control device mentioned above, the driving apparatus for driving the air-flow control valve has a solenoid actuator that opens the valve when the engine starting operation completes. The solenoid actuator, however, complicates the construction of the driving apparatus and increases the cost thereof.